(a) Field of the Disclosure
The present disclosure relates to an automatic transmission for a vehicle.
(b) Description of the Related Art
Research into realizing more shift-stages of an automatic transmission has been undertaken to achieve enhancement of fuel consumption and better drivability. Increased oil prices have triggering fierce competition to enhance or reduce fuel consumption for vehicles.
Therefore, research in the field of engines has been undertaken to achieve weight reduction and to enhance or reduce fuel consumption by so-called downsizing. Research in the field of automatic transmissions has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages.
In order to achieve more shift stages for an automatic transmission, the number of parts is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency.
Recently, an eight-speed automatic transmission has been introduced. Planetary gear trains for automatic transmissions enabling more shift stages are under investigation.
A conventional automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to seven engagement elements (frictional elements). Such a transmission may easily become lengthy, thereby deteriorating installability.
In this regard, solutions such as disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements have been attempted. However, such arrangements may not be widely applicable. Further, using dog clutches may easily deteriorate shift-feel.
The above information disclosed in this Background section is only to enhance understanding of the background of the disclosure. Therefore, the Background section may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.